We are investigating the neurobehavioral mechanisms that underlie auditory function and communication in crickets because these insects can serve as a model systems for understanding audition in higher animals. We are studying how crickets discriminate among potential mates and rivals, and how they detect and avoid predators, on the basis of acoustic signals. The simplicity of a cricket's auditory behavior and neural pathways permits a cellular analysis of how auditory information is processed and translated into adaptive behavioral acts. The well-known acoustic startle response (ASR) of mammals has numerous parallels in the ultrasound ASR of flying crickets. Moreover, the AsR in crickets can serve as a model system to investigate mechanisms of auditory processing that are ordinarily studied in mammalian audition, such as the precedence effect, habituation, prepulse inhibition, sensitization, and categorical perception. In the cricket, the neural basis underlying this processing is subserved by much simpler neural systems. Behavioral plasticity occurs in audition and likely involves neuromodulatory mechanisms. The simplicity of the cricket's auditory system, and our knowledge of the cellular relationships in the neural network underlying audition, provides an accessible experimental system for the investigation of neuromodulation of audition at the cellular level. The auditory behavior of crickets can be modified by manipulation of stimulus conditions; the extent to which biogenic amines are involved in modulating behavioral plasticity will be investigated. Hearing has evolved many times in insects and has produced a wealth of novel auditory mechanisms for both the detection and directionality of a sound source. Tympanal hearing has recently been found in an acoustic parasitoid fly. The structure and function of its hearing organ challenges our understanding of how an ear extracts directional information from a sound source. The opportunity to learn how other species solve such a primary problem is a fundamental benefit of making comparative studies of hearing, and these may lead to insights that touch basic issues in hearing.